1. Field of the Invention
This invention relates to a detergent composition containing alkaline pullulanase which has excellent detergency especially against starch soil.
2. Description of the Background Art
It is a known art that enzymes are compounded into a detergent composition The enzymes in the detergent composition act as a wash-aiding agent. They decompose or denature various kinds of soil and stain adhered to clothes, fats and oils, proteins, starch and the like remained on the dish surface to facilitate removal of the stains.
Heretofore, .alpha.-amylase has been used in order to remove starch soils. Detergency against starch soils is improved by soaking the washes in a washing solution containing .alpha.-amylase for a reasonably long time.
The inventors of the present invention found that a certain type of pullulanase effectively acted on starch soils adhered firmly to dishes and fibers, and enabled to improve the detergency remarkably (Japanese Patent Application Laid-Open (Kokai) No. 132192/1990).
However, almost all naturally occurring pullulanases are classified into neutral or acidic pullulanases which exhibit the maximal and stable enzymatic activity under the neutral or acidic pH conditions. Very few pullulanases exhibit the maximal activity or alkali-resistance in the alkaline pH range, which are suitable for a detergent composition for dishes or clothes.
An alkaline pullulanase in this invention means a pullulanase having an optimum pH in the alkaline range. An alkali-resistant pullulanase in this invention means a pullulanase having an optimum pH in the neutral to acidic range, and exhibiting still sufficient degree of activities even in the alkaline range when compared to the activity at its optimum pH while retaining a good stability. The terms `neutral` and `alkaline` are defined as the pH ranges of 6-8 and not less than 8, respectively.
Only alkaline pullulanase known heretofore is that disclosed in Japanese Patent Publication (Kokoku) No. 27786/1978. The above alkaline pullulanase is an enzyme having its optimum pH in the alkaline range and also having a wider substrate specificity than conventionally known pullulanases. However, since its optimum pH is in the weak alkaline range of 8-9, it is not applicable to a detergent component. In addition, the above pullulanase has disadvantages that the enzyme is unstable and has low productivity. Therefore, the above pullulanase is not suitable for the industrial fermentative production.
In view of this situation, the present inventors have carried out extensive studies in order to obtain pullulanases suitable as a detergent component, and, as a result, found that a detergent composition having detergency against starch soil was obtained by compounding an alkaline pullulanase which has its optimum pH in a high pH range and is not deactivated by surfactants. This finding has led to the completion of the present invention.